This invention relates to an optical disc playback device for playing back video data such as an LV (Laser Vision Disc) player or a CDV (Compact Disc with video) player and, more particularly, to an optical disc playback device capable of performing a still picture playback or still picture shifting of a CLV (constant linear velocity) disc frame by frame. The invention relates also to an optical disc playback device capable of realizing a uniform interval of changing of a picture throughout the entire circumferences of the disc from the innermost circumference to the outermost circumference during a fast/slow playback of a CLV disc.
In a prior art LV player, a still picture playback or a still picture shifting used to be made in a CAV (constant angular velocity) disc only. There has recently been developed an LV player which can perform a still picture playback or a still picture shifting in a CLV disc by incorporating a picture memory therein.
A still picture playback by using a picture memory is realized by storing picture data for one field or one frame in the picture memory and reading out this picture data repeatedly. A still picture shifting is realized by rewriting, each time a still picture shifting operation is made, contents of the picture memory by succeeding picture data (in the case of a forward still picture shifting) or preceding picture data (in the case of a backward still picture shifting) and reading out this data repeatedly.
In the prior art LV or CDV player, a picture memory writing control and an optical pickup jump control in a still picture playback or still picture shifting are made by utilizing a rotation signal which is obtained once per one rotation of a disc motor. More specifically, in a still picture playback, picture data for one field (or one frame) obtained for the first time after a still picture command has been given and a rotation signal has been supplied is stored in a picture memory and this data is repeatedly read out as still picture data. During the still picture playback, a tracking actuator of an optical pickup is provided with a jump pulse of a backward direction each time the rotation signal is given whereby the optical pickup jumps one track in the backward direction (i.e., toward the innermost circumference) and continues to trace the same track.
When a still picture shifting command has been given in a still picture playback mode, the optical pickup advances to trace a next track without making a jump upon receipt of the rotation signal if the command is one in a forward direction and the contents of the picture memory are rewritten by picture data for one field (or one frame) which is obtained first and this data is repeatedly read out. Upon finishing of the still picture shifting in the forward direction, the mode is brought to the still picture playback mode again and the jump pulse in a backward direction is given each time the rotation signal is supplied whereby the optical pickup jumps one track behind to trace the same track.
In the case of a still picture shifting in a backward direction, the optical pickup jumps two tracks in the backward direction (i.e., toward the innermost circumference) upon receipt of the rotation signal and the contents of the picture memory are rewritten by picture data for one field (or one frame) which is obtained first and this data is repeatedly read out. Upon finishing of the still picture shifting in the backward direction, the mode is brought to the still picture playback mode again and a jump signal in the backward direction is given each time the rotation signal is supplied whereby the optical pickup jumps one track behind to trace the same track.
A fast/slow playback is another type of trick play mode in an optical disc playback device. In the fast/slow playback, an optical disc is played back with a playback speed which is different from a normal playback speed. The fast/slow playback is realized by playing back a disc while performing a track jump at a predetermined interval. The multiplying number of fast or slow playback speed can be changed by changing the amount of one tracing, direction of jump and number of tracks to be jumped.
In a prior art LV player, fast/slow playback used to be made in a CAV disc only. There has recently been developed an LV player capable of performing fast/slow playback in a CLV disc by incorporating a picture memory therein.
In the prior art LV player and CDV player, a picture memory writing control and an optical pickup jump control in a fast/slow playback mode are made by utilizing a rotation signal obtained once per one rotation of a disc motor. More specifically, in a treble speed fast playback in a forward direction, for example, a tracking actuator of an optical pickup is provided with a jump pulse in a forward direction to jump two tracks toward the outermost circumference and picture data for one field (or one frame) obtained for the first time after the jump is stored in the picture memory and this data is repeatedly read out.
In an LV of a CLV disc type, picture data of one frame is recorded in one circumference in the innermost circumference of the disc and picture data of three frames is recorded in one circumference in the outermost circumference of the disc. In the prior art still picture playback and still picture shifting, one frame only is used for one circumference of the disc and, as a result, change of the picture in the still picture shifting becomes more coarse as the still picture shifting proceeds towards the outermost circumference of the disc (for example, only 10 frames are utilized in the outermost circumference notwithstanding that there are 30 frames per second).
In the fast/slow playback also, the same number of tracks are jumped for one circumference in the disc in the prior art LV player regardless of whether it is the innermost circumference or the outermost circumference with a result that, as the fast/slow playback proceeds toward the outermost circumference, the interval of jump becomes longer and, accordingly, the number of frames to be jumped by one jump becomes larger and change of the picture becomes more coarse.
It is, therefore, an object of the invention to provide an optical disc playback device capable of performing a still picture playback and a still picture shifting in a CLV disc frame by frame.
It is another object of the invention to provide an optical disc playback device capable of realizing a uniform change in the picture during a fast/slow playback of a CLV disc throughout the entire circumferences of the disc.